This invention relates in general to web drive mechanism and in particular to a ribbon drive mechanism for ink ribbons employed in a ribbon cartridge in serial printer applications.
Although the invention is applicable to various web, tape, strand and ribbon-like materials, it has been found particularly useful in the environment of ink ribbons as used in serial printers. Therefore, without limiting the meaning of the word "ribbon," the invention will be described in this environment.
In the particular environment of ink ribbons employed in ribbon cartridges in serial printers, it is normally necessary to provide a ribbon drive means by which force is applied to the ribbon to remove it from the receptacle providing the supply of ribbon. This same ribbon drive means provides the force to move or advance the ribbon past a print position during the printing operation. In most instances, ribbon take-up drive means for the take-up receptacle is required to provide the force necessary to place the ribbon on the receiving receptacle upon its deliverance or transfer from the supply receptacle. In some instances, the ribbon drive means and the ribbon take-up drive means comprise a single means, which performs both functions.
Also, normally a ribbon tension means is provided for maintaining a predetermined amount of tension in the ribbon material during its transfer from the supply receptacle to the take-up receptacle. Tension in the ribbon during its transfer is necessary for proper ribbon feed and ribbon position at the printing station or position to assure acceptable print quality of the printed material.
The amount of ribbon movement for each printing operation is dependent upon the particular pitch chosen and the particular type of ribbon being used. When print quality is of concern, the ribbon used will preferably be either a multi-strike ribbon or a single-strike ribbon. The multi-strike ribbon is designed so that a type font or slug can overstrike the same general area of the ribbon a number of times without loss of print quality. The first time the ribbon is impacted, a predetermined percentage of the ink is released; the next time the ribbon is impacted, another predetermined percentage of the ink is released, etc., until the maximum amount of ink is released from the ribbon without loss of print quality. The function of the ribbon drive is to advance or pull the ribbon the correct increments so that the overstrike area is used to maximum efficiency without loss of print quality. The single-strike ribbon is designed so that one impact by the type slug fractures the ink layer and essentially removes all the ink and transfers the ink from the ribbon to the paper. The next character to be printed must be impacted against a fresh portion of the ribbon. In this case, the ribbon drive must advance the ribbon a sufficient distance such that the next character impacts a fresh portion of the ribbon. It is obvious that the ribbon drive for the single-strike ribbon must advance a greater amount of ribbon per character printed than the driver used for the multi-strike ribbon.
In providing a ribbon drive means to advance the ribbon the desired amount between successive print operations, it is well known in the art to provide a drive roller with pointed projections thereon in conjunction with spring means for applying the drive force to the outer periphery of the ribbon wound on the take-up spool. It is also known to provide a pawl and ratchet arrangement for rotating the spindles, which rotatably support the ribbon supply spool and the ribbon take-up spool. In addition, it is known to provide a drive roller and a cooperating friction or pressure roller to pinch the ribbon therebetween and advance the ribbon as the drive roller or meter is rotated.
Such prior art solutions have utilized complex mechanical means comprising many elements in conjunction with various spring means to provide the necessary control of the drive means to transfer the web or ribbon material from the supply spool to the take-up spool.
With the prior art in mind, it is an object of the present invention to provide an improved ribbon drive means, which is compatible with cartridges of the present type.
Another object of this invention is to provide a cost effective ribbon drive means for ink ribbons contained in cartridges along the presently described type.
Other objects and advantages of this invention will be evident from the specification and claims in conjunction with the accompanying drawing illustrative of the invention.